In order to prevent a reduction in yield in a manufacturing line of microdevices, such as semiconductor devices, it is necessary to keep the interlayer overlay accuracy of overlay exposure at a high level by overlaying circuit patterns or the like in several layers onto a substrate such as a wafer or the like (hereinafter, referred to as a wafer), to form by pattern transfer shot areas in a lithography process.
When the overlay exposure is performed using a plurality of exposure apparatuses, an error between the stage grids of the exposure apparatuses (an error between stage coordinate systems for defining the movement position of the wafer in each exposure apparatus) may occur, which is a factor causing a reduction in the overlay accuracy. Even when the error between the stage grids of the exposure apparatuses is so small as to be negligible or the same exposure apparatus is used to expose the layers, the arrangement of shot areas on the previous layer may be distorted in the wafer subjected to processes such as, resist coating, development, etching, CVD (chemical vapor deposition), and CMP (chemical mechanical polishing), due to the processes. The distortion may cause a reduction in the overlay accuracy.
When a linear error occurs in the arrangement grid of shot areas on the previous layer of the wafer, the linear error is removed by an EGA (enhance global alignment) wafer alignment of measuring coordinates of only a plurality of sample shot areas selected beforehand (three or more sample shot areas, for example, 7 to 15 sample shot areas are needed) among shot areas on a wafer and calculating coordinates of all shot areas (arrangement coordinates of shot areas) on the wafer on the basis of the measured result by using a statistical operation (least square method or the like), which makes it possible to accurately perform the overlay exposure (for example, see Patent Document 1). However, when non-linear components of the grid cannot be negligible, it is difficult to remove the non-linear components by using the EGA wafer alignment.
Therefore, an exposure apparatus having a grid correcting function (a first grid correcting function) has been proposed (for example, see Patent Document 2). The grid collecting function measures a larger number of positional information of shot areas on, for example, a predetermined number of wafers counting from the head of each lot than that in the EGA wafer alignment, extracts non-linear components of the grid detected on the basis of the actually measured value of the positional information obtained by the measurement, regards the non-linear components as substantially the same between the wafers in a lot, and corrects the position of a wafer for the arrangement coordinates of all shot areas on each of the subsequent wafers in the lot that are obtained by a conventional EGA wafer alignment, using the non-linear components extracted from a predetermined number of wafers from the head of the lot as correction information, thereby performing overlay exposure.
The exposure apparatus disclosed in Patent Document 2 also has a correction function (a second correction function) of loading, for example, a reference wafer or the like having a plurality of shot areas arranged in an array along a reference grid, which is a reference of overlay exposure for exposure apparatus, into each exposure apparatus before lot processing, extracting non-linear components of the grid defined by the detection result of the reference grid, and correcting the position of a stage such that exposure is performed in a state aligned with the reference grid.
In the exposure apparatus, the first correction function or the second correction function is selected according to a variation in overlay error between a plurality of lots that are continuously processed in the exposure apparatus. The selection is performed to reduce the number of times the shot areas are measured to measure coordinates, from the viewpoint of preventing reduction in throughput. For example, when the variation in overlay error between a plurality of lots that are continuously processed in the exposure apparatus is relatively small, it is possible to regard the non-linear components of the grid in the exposure apparatus as being substantially the same between the lots. Therefore, in this case, the non-linear components of the lot previously processed are used as non-linear components of a lot currently processed, which makes it possible to perform the selection so as to reduce the number of times the shot areas are measured.
However, in recent years, it is necessary to perform overlay exposure considering high-degree non-linear components of the grid, in order to improve overlay accuracy. With the balance between the above-mentioned background and throughput, several correction function in which degree of non-linear components of a grid that can be considered are different have been proposed, so that the correction functions are more diversified and subdivided. Therefore, as described above, it is insufficient to use only the variation in the overlay error among a plurality of lots continuously processed in the exposure apparatus as a standard for the selection of the correction function, and thus a new selection standard capable of selecting an optimum function from a plurality of correction functions on the basis of accurate determination is needed.
Patent Document 1: U.S. Pat. No. 4,780,617
Patent Document 2: U.S. Published Application No. 2002/0042664